Nature of hydrogen-bond-enhanced halogen bonding viewed through electron density changes

Area of Science:

• Chemistry
• Molecular Interactions
• Computational Chemistry

Background:

• Fine-tuning intermolecular interaction strength is crucial for designing functional molecules.
• Halogen bonding is a significant non-covalent interaction.
• Hydrogen-bond-enhanced halogen bonding suggests synergistic effects.

Purpose of the Study:

• To theoretically analyze the electron density changes in halogen-bonded systems.
• To elucidate the mechanism behind enhanced halogen bond strength due to hydrogen bonding.
• To investigate the relationship between halogen bond strength and directionality.

Main Methods:

• Theoretical analysis of electron density.
• Examination of two specific iodinated halogen-bonding systems.
• Analysis of electrostatic potential and electron distribution anisotropy.

Main Results:

• Contrary to expectations, the anisotropy of electron distribution on the iodine atom remained largely unchanged.
• The hydrogen bond and halogen bond contribute independently and additively to electrostatic potential enhancement.
• The observed enhancement in electrostatic potential is explained by independent contributions.

Conclusions:

• Hydrogen bonding and halogen bonding act additively, not synergistically, in enhancing electrostatic potential.
• The directionality of halogen bonding is not significantly altered by the presence of a hydrogen bond.
• This finding clarifies the nature of hydrogen-bond-enhanced halogen bonding and its implications for molecular design.